The present invention relates to the field of downhole oil, gas, and/or geothermal exploration and more particularly to the field of detecting magnetic flux proximate a downhole tool string or drill string employed in such exploration.
For the past several decades, engineers have worked to develop apparatus and methods to effectively obtain information about downhole formations and the position and inclination of tool strings, especially during the drilling process. Various sensors and methods have been developed to obtain and transfer information to the surface.
U.S. Pat. Nos. 5,170,566 to Fowler et al., 4,623,842 to Bell et al., and 4,349,781 to Vozoff, each of which is herein incorporated by reference for all that it contains, describe sensors adapted to detect changes in magnetic fields. U.S. Pat. No. 6,216,533 to Woloson et al., herein incorporated by reference for all that it contains, describes a magnetic sensor for use in downhole applications. U.S. Pat. Nos. 5,466,614 to Yokosawa et al., 5,187,438 to Alcouffe et al., and 5,475,306 to Ludeke et al., each of which is herein incorporated by reference for all that it contains, describe devices for shielding magnetic sensors.
U.S. Pat. Nos. 7,265,649 to Hall et al., and 7,301,429 to Hall et al., each of which is herein incorporated by reference for all that it contains, disclose inductive downhole resistivity tools adapted to detect magnetic flux proximate a tool string.